Us cpa career

Will the visa stamping people give me enough time to write the CPA exams after getting NTS as it is known that it can be for 18months rolling period (max) to complete the exams or any extension needs to be applied if they stamped for 6months. And do I need to tell them any relative or friend sponsoror there to look after me for these period. pls suggest me how much time they award to me to complete the exams.